1
2
3
4	“Geography without geodesy is a felony”
5	Positioning Accuracy Standards Workshop Outline Introduction Definitions Evolution of Accuracy Standards Classical Surveying Standards GPS Surveying Standards Development of New Accuracy Standard Implementation of New Accuracy Standards Guidelines & Procedures Documents Computations/Software Data Publications Summary/Future
6	Definitions
7	Definitions Survey Standard Survey Specifications Precision Accuracy
8	What is a SURVEY STANDARD?
9	What is a Survey Standard? (Some Previous Responses) A level of precision of closure A reasonably accepted error A numerical limit on the uncertainty of coordinates Position relative to other points Such as 0.1 (units) + X ppm
10	Survey Standards Survey standards may be defined as the minimum accuracies deemed necessary to meet specific objectives. For the present, the practice of defining these criteria by the maximum acceptable uncertainty in length and/or position and assigning some nomenclature to them will be continued.
11	Why Do Surveyors Need Accuracy Standards?
12	Why Do Surveyors Need Accuracy Standards? (Some previous responses) To provide quality assurance of accuracy Such as within 8 mm + 1 ppm; 5 cm; 0.5 m To provide consistency To re-establish survey monuments
13
14
15
16
17
18
19
20
21
22	Survey Specifications Specifications can be described as the field operations required to meet a particular survey standard. Also included are the specified precision and allowable tolerances for the data collected, the limitations of the geometric form of acceptable figures, monumentation, and description of the points.
23	Definition of Precision precision (1) In statistics, a measure of the tendency of a set of random numbers to cluster about a number determined by the set. The usual measure is either the standard deviation with respect to the average, or the reciprocal of the quantity. It is distinguished from accuracy by the fact that the latter is a measure of the tendency to cluster about a number not determined by the set but specified in some other manner. From: Geodetic Glossary, National Geodetic Survey, September 1986
24	Standard Error of the Mean
25	Definition of Accuracy accuracy (1) Closeness of an estimated (e.g., measured or computed) value to a standard or accepted value of a particular quantity. Accuracy is commonly referred to as “high” or “low” depending on the size of the differences between the estimated and the standard values. (2) The square root of the average value of the sum of the squares of the differences between the values in a set and the corresponding values that have been accepted as correct or standard. (3) The reciprocal of the quantity defined in (2). Accuracy cannot be calculated solely from values based on measurements. A standard value or set of standard values must be available for comparison somewhere in the chain of calculations. The standard of reference may be: (a) an exact value, such as the sum of the three angles of a plane triangle being exactly 180°; (b) a value of a conventional unit as defined by a physical representation thereof, such as the international meter; (c) a value determined by refined methods and deemed sufficiently near the ideal or true value to be held constant, such as the adjusted elevation of a permanent bench mark or the graticule of a map projection. From: Geodetic Glossary, National Geodetic Survey, September 1986
26
27	CLOSURE
28	Examples of Closure
29	EVOLUTION OF ACCURACY STANDARDS
30
31	CLASSIFICATION OF CONTROL
32
33
34
35	HORIZONTAL CLASSIFICATIONS
36	What Does First-Order Horizontal Accuracy Mean?
37	20 Percent Rule
38	Types of Figures Where It May Be Difficult to Obtain Satisfactory Closures
39	What Does First-Order Horizontal Accuracy Mean? (When the points aren’t directly connected)
40	Accuracy Standards for Vertical Control
41	What Does First-Order, Class II Accuracy Mean?
42	What Does Second-Order, Class I Accuracy Mean? (When the points aren’t directly connected.)
43
44	Accuracy Standards for GPS
45	What Does B-Order GPS Accuracy Mean? (for “long” lines)
46	What Does B-Order GPS Accuracy Mean? (for “short” lines)
47
48
49	Summary of Previously Existing Accuracy Standards Triangulation & Traverse Directly Proportional to Distance Between Points i.e., 1 part per 100,000, 1:100,000 “Seldom to Exceed” Leveling Directly Proportional to SQRT of Distance Leveled i.e., Y mm X SQRT [Distance in km] “Seldom to Exceed” GPS Base Error + Directly Proportional to Distance Between Points i.e., 0.8 cm +1:1,000,000 At 95% Confidence Level
50	Development of New Accuracy Standards Federal Geodetic Control Subcommittee Federal Geographic Data Committee
51	Proposal for Geodetic Accuracy Standards
52
53
54
55
56
57	FGDC Subcommittees Base Cartographic (Interior - NMD) Bathymetric (Commerce - NOS) Cadastral (Interior - BLM) Cultural and Demographic (Commerce - Census) Geodetic (Commerce - NOS) Ground Transportation (Transportation - FHA) (State - Cartography) International Boundaries Soils (Agriculture - SCS, NRCS) Vegetation (Agriculture - Forest Service) Wetlands (Interior - Fish & Wildlife)
58	Why New Accuracy Standards Are Needed Accuracy of different types of spatial data (e.g., survey, cartographic, etc.) were described differently Accuracy of geodetic (survey) spatial data determined using different methodologies Classical horizontal (e.g., triangulation and traverse) Classical vertical (e.g., leveling) GPS Accuracy of new survey technology (i.e., GPS) is not consistent with classical accuracy methodology, (i.e., based on distance) Accuracy classification of survey data under old system not consistent with what GIS users want Local accuracy Network accuracy
59	New Direction FGDC Document: Geospatial Positioning Accuracy Standards (Only applies to POINT DATA !!!) Introduction Accuracy Standard Part 1 - Geodetic Networks Geodetic Subcommittee Part 2 - National Standard for Spatial Data Accuracy National Spatial Data Accuracy Standard Map Accuracy Standards Base Cartographic Subcommittee (continued)
60	FGDC Document: (continued) Geospatial Positioning Accuracy Standards Part 3 - Navigation Charts and Hydrographic Surveys Bathymetry Subcommittee Part 4 - Engineering, Construction & Facilities Management Facilities Working Group Part 5 - Cadastral and Boundary Surveys & Plats Cadastral Subcommittee Others ??? FGDC = Federal Geographic Data Committee
61	Accuracy Standard Components: Horizontal: Radius of circle 95-percent confidence level [Leenhouts, P. P. (1985) “On the computation of bi-normal radial error” Navigation, 32(1), 16-28] Vertical: Linear value 95-percent confidence Reported in: Metric units (preferred) English units (permitted) (continued)
62	Accuracy Standard (continued) Methodology used to determine accuracy values For example: least squares adjustment Must define how accuracies are achieved Accuracy level versus application Connection to National Datums: NAD83 NAVD88 (preferred) / NGVD29 (permitted) Other ?? Must state datum or include transformations
63
64
65
66
67
68
69
70
71	Local Accuracy
72	Network Accuracy
73
74
75	Improving Positional Accuracy
76	SUMMARY New Standards for Geodetic Control Networks Two accuracy standards Local accuracy (adjacent points) Network accuracy (relative to CORS) Numeric quantities, units of cm (or mm) Both are relative accuracy measures Do not use distance dependent expression Accuracies for horizontal, ellipsoidal, and orthometric height Horizontal accuracies are radius of 2-D 95% error circle Height accuracies are 1-D (linear) 95% error
77	IMPLEMENTATION OF NEW ACCURACY STANDARDS
78	Implementation of New Accuracy Standards Information Material/Workshop Guidelines & Procedures Documents Technical Memorandums In-house Procedures Computations/Software Program ADJUST Blue Book Readjustment of NAD 83 Data Publication Data Base Data Sheet
79
80
81
82
83
84	NAD 83 READJUSTMENT HARN COMPLETION - SEPTEMBER 1997 (Indiana) GPS HEIGHT MODERNIZATION OBSERVATIONS (1997 - 2004?) (Oklahoma Observed 1999) (http://www.ngs.noaa.gov/initiatives/height_modernization.shtml) COMPLETE GPS NAD 83 3-D ADJUSTMENT (http://www.ngs.noaa.gov/initiatives/new_reference.shtml) (2005?) REMOVAL OF SMALL REGIONAL DISTORTIONS (3 - 6 CM) UNIFORM COORDINATE TAG NAD 83 (NSRS)
85	NAD 83 READJUSTMENT
86	NAD 83 READJUSTMENT ONLY GPS DATA CONTINUOUSLY OPERATING REFERENCE STATIONS FEDERAL BASE NETWORK COOPERATIVE BASE NETWORK AIRPORT SURVEYS USER DENSIFICATION NETWORK SPECIAL SURVEYS
87	NAD 83 READJUSTMENT NAD 83 data that is NOT part of NSRS must be readjusted by contractor/user with original observations
88	NEW STANDARDS FOR GEODETIC CONTROL Two accuracy standards (http://fgdc.er.usgs.gov/standards/status/swgstat.html) local accuracy ------------- adjacent points network accuracy ---------- relative to CORS Numeric quantities, units in cm (or mm) Both are relative accuracy measures Do not use distance dependent expression Horizontal accuracies are radius of 2-D 95% error circle Ellipsoidal/Orthometric heights are 1-D (linear) 95% error
89
90	Data Sheet Issues That Need Resolving Network Accuracies How to compute horizontal accuracies for points determined by “classical” methods, e.g., triangulation and traverse stations What value to publish for orthometric heights determined by leveling How to identify the source of the accuracies, e.g., results of a rigorous least-squares adjustment, empirical formula, etc. Local Accuracies How to compute horizontal accuracies for points determined by “classical” methods, e.g., triangulation and traverse; should they be included in the “average” How to compute orthometric height accuracies for points determined by “classical leveling methods What values to include in computing the “average” How to identify the source of the accuracies, e.g., results of a rigorous least-squares adjustment, empirical formula, etc.
91	Tasks To Complete To Implement New Accuracy Standards Specify new data base elements Extend data base tables Update data sheet programs Define Blue Book accuracy records Update data base loading software Finalize “ADJUST/NETERR” program Develop new software adjustment program to compute accuracy estimates for orthometric heights from geodetic leveling measurements
92	Tasks (Continued) Identify CORS Develop realistic weights for GPS “New” GPS better than “old” GPS Depends upon processing/reductions Relative weight differences between horizontal and vertical Work supports writing GPS specifications Don’t need complete FBN/CBN to begin Work supports future scientific datum studies Error propagation of FBN/CBN network Network accuracies on points fixed in states May be possible on regional basis Work support future scientific datum studies
93	Summary/Future
94	Relationships to the Old Standards Local Accuracies Nearly identical to the old relative accuracies Do not use distance dependent expression Use weighted constrained adjustment instead of free adjustment Network Accuracies New measure --- represents confidence of that point with respect to geodetic datum Smaller values from distance dependent equations Compute by weighted constrained adjustment Compute by formulas for simple survey geometries
95	Where Do We Go from Here? Classification By: Order and Class is OUT Actual accuracy is IN Accuracy Expressed As: Proportional Part is OUT Linear units (cm) is IN Classification Scheme: Single classification is OUT Local and Network Accuracies are IN
96	Where Do We Go from Here? (continued) Accuracy Criteria: Using different methods for stating the accuracy of horizontal and vertical coordinates is OUT Using the same accuracy statement for horizontal and vertical coordinates is IN
97	Where Do We Go from Here? (continued) FGDC Publication: Defines just the accuracy standards Includes: Geodetic, Cartographic, Bathymetric, Engineering, and Cadastral NGS Publications: Uses FGDC accuracy standards Further explains FGDC standards as they apply to geodetic networks Provides guidelines, procedures, and specifications to meet various accuracy levels
98
99	Points of Contact National Geodetic Survey NOAA, N/NGS12 Geodetic Services Division Bldg. SSMC3, Station 9202 1315 East-West Highway Silver Spring, MD 20910-3282 Phone: 301-713-3242 Fax: 301-713-4171 Internet Web Site: http://www.ngs.noaa.gov David Doyle N/NGS2, SSMC-3, Room 8813 National Geodetic Survey, NOAA 1315 East-West Highway Silver Spring, MD 20910-3282 Phone: 301-713-3178 Ext. 117 Fax: 301-713-4324 E-mail: Dave.Doyle@noaa.gov
100
101